Peptidic antagonists of corticotropin releasing factor (CRF) and the urocortins (Ucn) have been critical in the understanding of endocrine, immune, cardiovascular and gastrointestinal functions in response to different stress stimuli. Nonpeptide CRF antagonists are developed for the treatment of depression. Further, the actual function, distribution and specificity of the two different CRF receptors (CRFR1 and CRFR2) and their subtypes are now better understood due to the availability of CRF-receptor-selective agonists and antagonists. However, significant amino acid sequence differences between the multiple CRF native ligands (CRF and Ucn 1, 2 and 3 in mammals) and the wide distribution of CRFR1 and CRFR2 with their concomitant modulation of multiple functions remain to be integrated and understood. There are two complementary end points to this Project: a) structural and b) pharmacological/biological. Both end points depend heavily on the synthesis of peptides (SPPS) and proteins (fragment chemical ligation). a) We propose to design and synthesize CRF/Ucn analogs and extra cellular domains 1 (ECD1s) of class B1 GPCR for functional and structural investigations using NMR in collaboration with Dr. Riek's project. Preliminary results have yielded a model of the interaction between the ECD1 of CRFR2 and the CRF antagonist, astressin B. Additional studies are mandatory to identify the actual contact points between ligands and the respective ECDs1 responsible for the initial steps of recognition and binding. This will be achieved with binding assays of mutated ECD1s and complementarily derivatized analogs of selected ligands. From these studies, we will derive consensus bioactive/binding conformations of the CRFR1 -selective and CRFR2-selective ligands and the pharmacophores of the respective receptors, b) We will use these pharmacophores in models for the rational design of novel peptide and nonpeptide CRFR1 and CRFR2 ligands. In particular, we propose to pursue the design of peptide CRFR1-selective antagonists using several approaches distinct from that used for the characterization of stressing a potent and CRFR1-selective agonist and astressin2-B, a potent and long acting CRFR2-selective antagonist. We will use these selective and potent reagents to identify through collaborations within this Program Project, and with outside investigators, the etiology of pathophysiological states for possible treatment.